Shafts are probably one of the oldest structural elements known to man, in the form of a long slender rod forming the body of a spear, the handle of a hammer, ax or golf club, and many other long implements. Modern aircraft use shafts to transmit motion, such as control rods. Most machinery use shafts to transmit motion in a push-pull or rotating action.
The major shortcoming of shafting used in advanced aircraft or high-speed rotating machinery is a low modulus of elasticity to density (stiffness to weight) ratio. This poor stiffness to weight ratio requires the use of mid-support bearings or other mechanical devices which greatly increase weight, waste power and complicate design. One method of increasing the modulus and reducing the weight of a metal shaft is to reinforce it with a higher modulus and lower density material. Another characteristic necessary for the reinforcement is ductility sufficient for redistribution of stresses.
Many shafts are subject to impact loading, for example, connecting rods in a reciprocating engine, transmission shafts in a helicopter, and control rods in an aircraft. Previous work has proven that the metal beryllium used as a reinforcement in a metal matrix composite is superior to all other plastic and metal matrix composites when subject to impact loads. The lack of ductility has proven to be a serious limitation in boron aluminum, boron epoxy and carbon epoxy type composites. In addition, the excellent elevated temperature ductility of beryllium allows fabrication procedures to be employed which could not be considered for less ductile composite systems.
Others have employed beryllium fiber, filaments and wires as reinforcing material. The diameter of this wire has not exceeded 0.01 inches and is quite costly to make, almost $4,000per pound. In my previous U.S. Pat. No. 3,609,855 and U.S. Pat. No. 3,667,108 and in my parent application Ser. No. 256,491, methods and techniques for the production of beryllium ribbon-reinforced composites and beryllium-titanium blading were disclosed. This invention is related to those methods but instead is directed to hollow and solid composite shafting.